It is known in the art relating to flexplate engine flywheels to provide a thin annular ring fixed as by projection welding to the flexplate inwardly of an associated starter ring gear to reduce engine generated flexplate vibrations that may result in undesirable sound transmitted from the flywheel and/or engine. One such prior art arrangement which has been used commercially in automobiles for connecting the engine with a transmission is shown in FIGS. 1 and 2.
In these Figures, numeral 10 indicates the prior art flywheel which comprises a circular disc 11 of rotatably stiff but axially flexible relatively thin sheet metal. The disc 11 is of generally constant axial thickness although variable thickness discs could be provided if desired. The disc 11 has a generally flat outer annulus 12 contacted with a slightly dished central portion 14 having a central guide opening 15 surrounded by a plurality of smaller openings 16 for attaching the disc 11 to a flanged end 18 of an engine crankshaft 19. The degree of dishing is optional and depends primarily upon the space available between the crankshaft 19 and an associated transmission input member such as a fluid coupling 20.
Beyond the outer annulus 12, the disc 11 has a short axial flange 21 to which is intermittently welded at 22 a steel ring gear 23 having outwardly facing teeth 24 adapted to be engaged by a starter drive gear 26 for starting the engine. (Some prior art arrangements omit the flange 21 and weld the ring gear directly to the flat outer annulus 12 of the disc.)
Between the flange 21 and the central portion 14 a damping ring 27 formed as a thin generally flat annulus is fixed at radially and annularly spaced locations 28 by projection welding or the like to the flat outer annulus 12. Annularly spaced mounting openings 30 extend through the outer annulus 12 and damping ring 27. One opening 30A may be nonround for balancing alignment of the engine and transmission upon assembly. Additional openings 31 may be provided through the disc 11 for controlling its stiffness and lightening the flywheel 10.
The prior arrangement as described for FIGS. 1 and 2 has been effective in reducing or altering engine generated sound vibrations to provide quieter or more pleasing engine and vehicle noise transmission within and outside the vehicle. However, a further reduction in starter drive generated noise to obtain an improved perception of transmitted sound was also desired.